Back to EveryPatent.com
United States Patent |
5,565,397
|
Sangokoya
|
October 15, 1996
|
Olefin polymerization catalyst comprising a metallocene and an anhydrous
lithium halide-treated alkylaluminoxane
Abstract
Alkylaluminoxanes having improved catalytic activity such as when they are
used in combination with metallocenes for the polymerization of
alpha-olefins, are prepared by treating an organic solvent solution of an
alkylaluminoxane, such as methylaluminoxane, with anhydrous lithium
halide.
Inventors:
|
Sangokoya; Samuel A. (Baton Rouge, LA)
|
Assignee:
|
Albemarle Corporation (Richmond, VA)
|
Appl. No.:
|
440037 |
Filed:
|
May 12, 1995 |
Current U.S. Class: |
502/129; 502/111; 502/117; 502/152; 502/154; 526/124.1; 526/160 |
Intern'l Class: |
C08F 004/606 |
Field of Search: |
502/103,129,111,117,152,154
526/123.1,124.1,160
|
References Cited
U.S. Patent Documents
5099050 | Mar., 1992 | Sangokoya | 556/179.
|
5117020 | May., 1992 | Razavi | 556/43.
|
5157137 | Oct., 1992 | Sangokoya | 556/179.
|
Primary Examiner: Delmendo; Romulo H.
Attorney, Agent or Firm: Pippenger; Philip M.
Parent Case Text
This application is a division of application Ser. No. 08/123,779, filed
Sep. 20, 1993, now abandoned.
Claims
What is claimed is:
1. An olefin polymerization catalyst comprising a metallocene and an
alkylaluminoxane prepared by the process comprising treating an organic
solvent solution of alkylaluminoxane, said alkylaluminoxane having been
prepared by adding free water to an organic solvent solution of
alkylaluminum, with anhydrous LiX, wherein X is selected from the group
consisting of chloride, fluoride and bromide, in proportions of at least
about 0.01 mole of LiX per mole of aluminum in the alkylaluminoxane.
2. The catalyst of claim 1 wherein said alkylaluminoxane is
methylaluminoxane.
3. The catalyst of claim 1 wherein said solvent is an aromatic hydrocarbon.
4. The catalyst of claim 3 wherein said solvent is toluene.
5. The catalyst of claim 2 wherein said LiX is used in proportions of from
about 0.01 to 0.2 moles of LiX per mole of aluminum in the
methylaluminoxane.
6. The catalyst of claim 1 wherein the mole ratio of metal atom in said
metallocene to aluminum atom in said alkylaluminoxane is from about
0.0002:1 to 0.2:1.
7. The catalyst of claim 1 wherein the mole ratio of metal atom in said
metallocene to aluminum atom in said alkylaluminoxane is from about
0.0005:1 to 0.2:1.
Description
This invention relates generally to alkylaluminoxanes and more specifically
to alkylaluminoxanes having both increased solubility in organic solvents
and increased catalytic activity which are prepared by treating
alkylaluminoxanes with anhydrous lithium halide salts.
My U.S. Pat. No. 5,157,137 relates to a process for forming clear, gel free
solutions of alkylaluminoxanes by treating a solution of the
alkylaluminoxane with an anhydrous salt and/or hydroxide of an alkali or
alkaline earth metal. I now have found that alkylaluminoxanes treated with
anhydrous lithium chloride, bromide or iodide have both improved organic
solvent solubility and improved catalytic activity when used in olefin
polymerization.
In accordance with this invention there is provided an alkylaluminoxane
having improved catalytic activity prepared by the process comprising,
treating an organic solvent solution of alkylaluminoxane with anhydrous
LiX, where X is selected from chloride, fluoride, and bromide.
Also provided is an olefin polymerization catalyst comprising a metallocene
and an alkylaluminoxane obtained by treating an organic solvent solution
of alkylaluminoxane with anhydrous LiX, wherein X is selected from the
group consisting of chloride, fluoride and bromide.
Also provided is an olefin polymerization process comprising contacting an
olefin monomer having from 2 to 20 carbon atoms, including mixtures
thereof, under polymerization conditions with a catalyst comprising a
metallocene and an alkylaluminoxane prepared by treating an organic
solvent solution of alkylaluminoxane with anhydrous LiX, wherein X is
selected from the group consisting of chloride, fluoride and bromide.
Hydrocarbylaluminoxanes may exist in the form of linear or cyclic polymers
with the simplest compounds being a tetraalkylaluminoxane such as
tetramethylaluminoxane. (CH.sub.3).sub.2 AlOAl(CH.sub.3).sub.2, or
tetraethylaluminoxane, (C.sub.2 H.sub.5).sub.2 AlOAl(C.sub.2
H.sub.5).sub.2. The compounds preferred for use in olefin polymerization
catalysts usually contain about 4 to 20 of the repeating units:
##STR1##
where R is C.sub.1 -C.sub.8 alkyl including mixed alkyl, and especially
preferred are compounds where R is methyl. Methylaluminoxanes (MAO's)
normally have lower solubility in organic solvents than higher
alkylaluminoxanes and the methylaluminoxane solutions tend to be cloudy or
gelatinous due to the separation of particles and agglomerates. This
problem is frequently encountered with MAOs which have been prepared by
adding free water, either neat or contained in a solvent, to a solution of
trimethylaluminum as described, for example, in Manyik et al. U.S. Pat.
No. 3,300,458. According to such processes, the water-alkylaluminum
reaction is carried out in an inert solvent. Any inert solvent can be
used. The preferred solvents are aliphatic or aromatic hydrocarbons.
Aromatic hydrocarbons are more preferred such as toluene, xylene,
ethylbenzene, cumene, mesitylene and the like. The methylaluminoxane
products usually contain up to 70% and usually from about 25 to 30 weight
percent of unreacted trimethylaluminum.
The invention provides more soluble and more catalytically active
alkylaluminoxanes by treating the cloudy or gelatinous MAO solutions,
which contain from about 0.5 to 30 weight percent aluminum values, with
anhydrous lithium chloride, fluoride or bromide, including mixtures
thereof, in proportions of at least about 0.01, and preferably from 0.02
to 0.2, moles of lithium salt per mole of aluminum in the
alkylaluminoxane. Larger portions of lithium salt can be used but are not
necessary.
The treatment can be accomplished by adding the salt to the
alkylaluminoxane solution with stirring for from about 1 to 4 hours at
ambient temperatures (15.degree.-30.degree. C.). The time is not
particularly critical, and longer or shorter times, which are effective to
provide a clear solution can be used. Higher or lower temperatures can
also be used.
After the treatment, the solids, including the treating compound, are
conveniently removed from the solution by filtration but they can also be
removed by any conventional liquid-solid separation techniques such as by
settling or centrifugation followed by decanting the liquid.
Because of the increased solubility resulting from the lithium halide
treatment, highly concentrated solutions of MAO (up to 50-60 weight
percent) in toluene are obtainable via this process. This is an important
advantage for storage (reduced capital expenditure on tanks) and overseas
shipment or transportation in general.
The soluble alkylaluminoxane and especially MAO products are used in
combination with a primary catalyst to form catalyst systems which are
useful in the dimerization, oligomerization and polymerization of olefins
including both aliphatic olefins such as ethylene, propylene, butenes and
the like and aromatic olefins such as styrene, and the like or the
reaction of other functional groups such as epoxides. Suitable primary
catalysts include but are not limited to metal acetylacetonates,
metallocenes including derivatives thereof and the like. Preferred primary
catalysts for olefin reactions are metallocenes and in such use the
treated MAO affords a significant improvement in catalytic activity.
The primary metallocene catalysts can be d.sup.0 organometallic compounds
of a transition metal such as titanium, zirconium or hafnium. As used in
this application the term "metallocene" includes metal derivatives which
contain at least one cyclopentadienyl moiety. The catalyst structure may
be described as metallocene (or bent metallocene in the case of
bis-cyclopentadienyl compounds) with ancillary anionic ligands or
hydrocarbyl groups, such as metallocenes of the formula Z.sub.t
(.eta..sup.5 -R'.sub.n H.sub.m C.sub.5).sub.s MX.sub.4-s, where R' is a
carbon or a carbon and heteroatom (N, O, S, P, B, Si and the like)
containing C.sub.1 to C.sub.6 alkyl, C.sub.3 to C.sub.12 cycloalkyl or
C.sub.6 to C.sub.14 aryl group. Non-limiting examples of such groups
include methyl, ethyl, trimethylsilyl, t-butyl, cyclohexyl, phenyl,
4-methylphenyl, 2,4,6-trimethylphenyl and the like. The R' substituents
can be different in type and number on each cyclopentadienyl ring and can
form fused cyclic groups attached to the ring. Z is a bridging group
between two cyclopentadienyl rings such as silane, phosphine, amine or
carbon groups, t is 0 or 1, m and n are integers of 0 to 5, m+n=5 when t
is 0 and 4 when t is 1, s is 1 or 2, M is the transition metal and X is
halogen, psuedohalogen, (e.g. a leaving group in nucleophilic substitution
such as ester, cyanide, tosylate, triflate, .beta.-diketonate and the
like), hydride or C.sub.1 to C.sub.8 alkyl. Analogous metallocenes with
two different X groups are also effective in the presence of an
aluminoxane. Also effective are bimetallic .mu.-oxo analogues such as
O[ClHf(C.sub.5 H.sub.5).sub.2 ].sub.2 and mono-cyclopentadienyl metal
trihalides.
These and other metallocenes are well known in the art and are described,
for example, in published European patent application No. 0 129,368 and
U.S. Pat. Nos. 5,017,714, 5,026,798 and 5,036,034, whose teachings with
respect to such metallocenes are incorporated herein by reference.
Specific non-limiting examples of metallocenes which are useful in forming
the catalysts of the invention include bis(cyclopentadienyl)zirconium
dichloride, bis(cyclopentadienyl)hafnium dichloride,
bis(pentamethylcyclopentadienyl)hafnium dichloride, bis(indenyl)hafnium
dichloride, bis(methylcyclopentadienyl)hafnium dichloride, racemic and
meso dimethylsilanyl bridged bis(methylcyclopentadienyl)hafnium
dichloride, bis(cyclopentadienyl)titanium dichloride,
bis(ethylcyclopentadienyl)zirconium dimethyl,
bis(.beta.-phenylpropylcyclopentadienyl)zirconium dimethyl,
bis(methylcyclopentadienyl)zirconium dimethyl, racemic dimethylsilanyl
bridged bis(indenyl)hafnium dichloride, racemic ethylene bridged
bis(indenyl)zirconium dichloride, (.eta..sup.5 -indenyl)hafnium
trichloride and (.eta..sup.5 -C.sub.5 Me.sub.5)hafnium trichloride, and
the like.
The catalyst components are used in proportions to provide mole ratios of
transition metal atom to aluminum atom of from about 0.0002:1 to 0.2:1 and
preferably 0.0005:1 to 0.02:1. The catalyst components can be used in
solution or deposited on a solid support. The solid support can be any
particulate solid, and particularly porous supports such as talc or
inorganic oxides, or resinous support material such as polyolefins.
Preferably, the support material is an inorganic oxide in finely divided
form.
Suitable inorganic oxide support materials which are desirably employed
include Group IIA, IIIA, IVA or IVB metal oxides such as silica, alumina,
silica-alumina and mixtures thereof. Other inorganic oxides that may be
employed either alone or in combination with the silica, alumina or
silica-alumina are magnesia, titania, zirconia, and the like. Other
suitable support materials are finely divided polyolefins such as finely
divided polyethylene.
The catalysts are effective to produce olefin polymers and especially
ethylene polymers and ethylene/.alpha.-olefin copolymers. Examples of
olefins that can be polymerized in the presence of the catalysts of the
invention include .alpha.-olefins having 2 to 20 carbon atoms such as
ethylene, propylene, 1-butene, 1-hexene, 4-methyl-l-pentene, 1-octene,
1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene.
Polymerization of ethylene or copolymerization with ethylene and an
.alpha.-olefin having 3 to 10 carbon atoms is preferable. Such
polymerizations may be performed in either the gas or liquid phase (e.g.
in a solvent, such as toluene, or in a diluent, such as heptane). The
polymerization can be conducted at conventional temperatures (e.g.,
0.degree. to 120.degree. C.) and pressures (e.g., ambient to 50
kg/cm.sup.2) using conventional procedures as to molecular weight
regulation and the like.
The invention is further illustrated by, but is not intended to be limited
to, the following examples.
The following examples were carried out under inert atmosphere conditions,
using Schlenk glassware and vacuum line, in conjunction with a N.sub.2
-drybox. Solvents were distilled using standard methods. Filtration and
vacuum distillation were done inside a N.sub.2 -drybox and distillates
were collected in a trap at -78.degree. C. Lithium halides were purified
by heating in a vacuum oven overnight. Aluminoxanes were obtained from
stock solutions produced by Ethyl Corporation.
EXAMPLE 1
A 10 wt % toluene solution of methylaluminoxane (MAO, 270 mmol Al) was
placed in a reaction flask, in a N.sub.2 -drybox. Lithium chloride (LiCl,
13.5 mmol) was added in batches during a period of about 15 minutes. After
addition, the mixture was stirred at room temperature for one hour. The
mixture was then heated at 70.degree. C. (oil bath) for another two hours.
Upon cooling, the mixture was filtered through a medium frit. Filtration
was relatively easy. Ordinarily it is very difficult to filter regular MAO
through a medium frit. The liquid product was divided into two parts. One
part was bottled for storage and the other part was further concentrated.
The initial product contained about 96% of the original aluminum value.
Both liquid products (12.6 wt % and 28.1 wt % MAO) remained gel free even
after 12 weeks. Ordinarily, a 10 wt % solution of MAO in toluene initiates
gelation after about one or two weeks. Additionally, the products are
found to be about 50% more active than regular MAO when used in
conjunction with zirconocene dichloride for ethylene polymerization (Table
3).
EXAMPLE 2
This procedure was performed to investigate the effectiveness of this
procedure in large scale reactions. A toluene solution of MAO (870 g, 1479
mmol Al) was placed in a reaction flask. LiCl (3.2 g, 74 mmol) was added
in batches. The mixture was stirred at room temperature for two hours
followed by heating at 70.degree. C. (oil bath) for another 3 hours.
Filtration through a medium frit was relatively easy. Soluble aluminum
value recovered was 92% of the original. The product was found to be very
active in ethylene polymerization (Table 3).
EXAMPLE 3
Lithium chloride (1.12 g, 26 mmol) was allowed to react with a solution of
MAO in toluene (120 g, 252 mmol Al), as described in Example 1, except
that the Al/LiCl mole ratio is 10 instead of 20. Analysis showed that 84%
of the original aluminum value was recovered. Chloride incorporation into
the MAO solution was also negligible. Tables 1 and 2 show product
analysis.
EXAMPLE 4
A 30 wt % solution of MAO in toluene (340 mmol Al) was treated with LiCl
(2.88 g, 68 mmol) as described in Example 1. Analysis of products is shown
in Tables 1 and 2. The product was found to be very active in ethylene
polymerization (Table 3). The increase in the amount of LiCl used did not
appear to have any adverse affect on the quality of the product.
EXAMPLE 5
This procedure was performed in order to investigate if a smaller amount of
LiCl would effectuate clarification and stabilization. A Al/LiCl mole
ratio of 0.02 was used. Thus a 10 wt % solution of MAO in toluene (204
mmol Al) was treated with LiCl (4 mmol) as described in Example 1. The
product was found to be very stable (Table 2) and active in ethylene
polymerization (Table 3). However, filtration was slightly difficult.
Therefore, larger amounts of LiCl are recommended for easy filtration.
EXAMPLE 6
All the above described examples used heat. This procedure investigated the
effect of the absence of heat in the quality of the product. A solution of
MAO in toluene (240 mmol Al) was treated with LiCl (12 mmol). The mixture
was stirred at room temperature for 14 hours and then was worked up as
described in Example 1. Filtration was difficult, but a clear ("water
white") solution was obtained. The product was found to be very active in
ethylene polymerization. Thus, heat provides an easily filtrable product
but had no apparent effect on the quality of the product.
COMPARATIVE EXAMPLE 1
No lithium chloride was used in this comparison in order to demonstrate the
effectiveness of the lithium salt treatment. A 10 wt % solution of MAO
(201 mmol Al) was filtered through a medium frit. Filtration was extremely
difficult. Only about 62% of the initial aluminum value was recovered in
the product. The results as reported in Table 2 shows that the clarity and
stability of the untreated products were clearly inferior to those which
had been treated with lithium salts. Furthermore, the activity in ethylene
polymerization was lower (Table 3).
COMPARATIVE EXAMPLE 2
No lithium salt was used in this comparison but heat was applied in order
to demonstrate the effect of heat on the MAO solution. A 10 wt % solution
of MAO in toluene (161 mmol Al) was heated at 70.degree. C. (oil bath) for
about four hours. The mixture was then worked-up as described in Example
1. Filtration was very difficult. The amount of recovered aluminum value
(74%) was improved in comparison with the comparative Example 1. However,
Table 2 shows that the stability of the product was inferior to the
lithium salt treated MAO solutions.
EXAMPLE 7
A 10 wt % solution of MAO (70 g, 153 mmol Al) was diluted with toluene (100
g). The solution was then treated with LiF (0.2 g, 7.7 mmol). The mixture
was stirred at room temperature for 4 hours. The mixture was initially
filtered through coarse frit and then through medium frit (slow and
difficult filtration). Due to the difficulty in filtration only 71% of the
original aluminum value was recovered. The product was found to be active
in ethylene polymerization (Table 3).
EXAMPLE 8
A 30 wt % MAO solution in toluene (294 mmol Al) was treated with LiF (58.8
mmol). After stirring at room temperature for one hour, the mixture was
heated at 80.degree. C. for 2 hours. A high density lower layer formed. On
cooling, this transformed to a cake-like solid layer, which contained most
of the aluminum value.
The procedure was repeated without heating. After filtration, only about
56% of the initial aluminum value was recovered as soluble aluminum but
the soluble product was found to be extremely active in ethylene
polymerization.
EXAMPLE 9
A 10 wt % solution of MAO in toluene (217 mmol Al) was treated with LiBr
(10.8 mmol) as described in Example 1. A small amount of thick oily-solid
gel appeared at the bottom of the reaction flask. The mixture was first
decanted and then filtered. Filtration was very easy. The liquid product
contained 76% of the original aluminum value. The product showed superior
activity compared to untreated MAO (Table 3).
COMPARATIVE EXAMPLE 3
Clarification of MAO solution in toluene was very effective using LiI.
Thus, LiI (1.1 g, 82 mmol) was added to a 10 wt % solution of MAO toluene
(163 mmol Al). The reaction was done as described in Example 9. The clear,
colorless liquid product was found to be stable even after 12 weeks.
However, this material is relatively inactive in ethylene polymerization.
It would appear that a small amount of contained iodide interferes with
the polymerization mechanism.
TABLE 1
__________________________________________________________________________
Treatment of Methylaluminoxane (MAO) With Lithium Halides (Product
Analysis)
Reaction.sup.1
Reagent/Al
Filtration.sup.2
Soluble Al
Mole Ratio
Example
Condition
Reagent
Mole Ratio
(Med. Frit)
Recovered \%
Al/Cl
__________________________________________________________________________
Example 1
A LiCl 0.05 E 96 63
Example 2
A LiCl 0.05 E 92 114
Example 3
A LiCl 0.10 E 84 49
Example 4
A LiCl 0.20 E 9 47
Example 5
A LiCl 0.02 SD 93 191
Example 6
B LiCl 0.05 D 83 77
Comp. Ex. 1
B -- -- VD 62 --
Comp. Ex. 2
A -- -- VD 74 --
Example 7
B LiF 0.05 D 71 --
Example 8
B LiF 0.20 NF 56 --
Example 9
A LiBr 0.05 E 76 --
Comp. Ex. 3
A LiI 0.05 E 72 --
__________________________________________________________________________
.sup.1 Reaction condition; A = Heat, B = No heat
.sup.2 Filtration; E = Easy, D = Difficult, SD = Slightly difficult, VD =
Very difficult, NF = Not filtered but decanted
TABLE 2
__________________________________________________________________________
Stability of Liquid Products
Initial Liquid Product Concentrated Liquid Product
Examples
Wt % MAO
TMA Content Mole %
Stability.sup.a (Weeks)
Wt \% MAO
TMA Content.sup.b Mole
Stability
__________________________________________________________________________
(Weeks)
Example 1
12.6 21 >12 28.1 15.8 >12
Example 3
11.4 22 >12 23.1 20 >12
Example 4
22.2 22 >12 7 20 >12
Example 5
9.7 18 >12 32.1 19 >12
Example 6
9.2 19 >12 39.6 12.4 >12
Comp. 10.9 25 <2 31.6 15 <1
Ex. 1.sup.c
Comp. 9.5 19 <4 30.2 16 <2
Ex. 2.sup.d
__________________________________________________________________________
.sup.a Defined as the time required for the appearance of gel or
precipitates.
.sup.b Defined as moles of aluminum as TMA (pyridine titration) with
respect to total aluminum content
.sup.c Regular MAO product subjected to filtration and concentration.
.sup.d Heated but no LiCl was added.
EXAMPLE 10
Polymerization of Ethylene
The products obtained from the above mentioned examples and comparative
examples were used in conjunction with zirconocene dichloride to
polymerize ethylene according to the following procedure.
Inside a N.sub.2 -drybox, an autoclave (600 ml) was charged with toluene
(250 ml). A mixture of the treated MAO product (10 mmol Al) and
zirconocene dichloride (6.8.times.10.sup.-6 mol) in toluene (50 ml) was
added. The autoclave was then brought out of the dry box and set up in a
hood. After reactor was heated to 80.degree. C., ethylene was introduced
at 60 psi during 10 minutes. The reaction was quenched by addition of
methanol (300 ml). The polyethylene produced was initially air dried,
followed by drying in a vacuum oven without heating. The yield of
polyethylene and the activity of the catalyst compositions are reported in
Table 3.
TABLE 3
__________________________________________________________________________
Ethylene Polymerization Lithium Halide Treated Methylaluminoxane (MAO)
MAO Zirconocene Dichloride
Al/Zr Activity (.times.10.sup.6)
Activity Compared to
Compositon (10 mmol Al)
(moles .times. 10.sup.-6)
mole ratio
Zr .multidot. atm .multidot. hr
Untreated MAO
PE
__________________________________________________________________________
(g)
Example 1 6.8 1470 9.51 1.57 44
Example 2 6.8 1470 8.87 1.46 41
Example 4 6.8 1470 8.00 1.32 37
Example 5 6.8 1470 9.30 1.54 43
Example 6 6.8 1470 9.51 1.57 44
Example 7 6.8 1470 8.65 1.43 40
Example 8 6.8 1470 11.24 1.86 52
Example 9 6.8 1470 9.30 1.54 43
Comp. Ex. 1 6.8 1470 6.05 -- 28
Comp. Ex. 2 6.8 1470 7.35 1.21 34
Comp. Ex. 3 6.8 1470 1.08 0.18 5
Comp. Ex. 3 6.8 1470 1.73 0.29 8
__________________________________________________________________________
Top